1. Field of the Invention
The present invention relates to a control valve device for a variable capacity type swash plate compressor, and the compressor is used in a refrigerating circuit of an air conditioning system disposed in a vehicle.
2. Description of the Related Art
A refrigerating circuit includes an evaporator and a condenser, and a variable capacity type swash plate compressor is disposed between the evaporator and condenser. This type of compressor is described, for example, in Japanese Unexamined Patent Publication No. 2001-107854. This known compressor has a crank chamber, and a swash plate is rotatably accommodated in the crank chamber. A tilt angle of the swash plate determines a discharge capacity of a refrigerant of the compressor, that is, reciprocating strokes of pistons in the compressor.
In this type of compressor, since the tilt angle of the swash plate is adjusted by a pressure in the crank chamber, the compressor includes an introducing passage connecting the crank chamber to a discharge chamber of the compressor, a release passage connecting the crank chamber to a suction chamber of the compressor and having an orifice, and a capacity control valve inserted in the introducing passage. The capacity control valve controls a flow rate of a high-pressure refrigerant introduced into the crank chamber from the discharge chamber, that is, the pressure in the crank chamber.
In more detail, the capacity control valve includes a valve unit and an electromagnetic solenoid assembly for operating the valve unit. The valve unit includes a valve member for opening/closing the introducing passage, and the valve member receives an electromagnetic force generated by the solenoid assembly in a closing direction of the valve member, while receiving an urging force based on a differential pressure of the refrigerant between two points defined between the compressor and condenser in an opening direction of the valve member.
Since the differential pressure of the refrigerant is an index indicating the discharge capacity from the compressor, the electromagnetic force is applied to the valve member in accordance with a target discharge capacity. Therefore, the valve member opens/closes the introducing passage so as to balance the electromagnetic force and urging force (discharge capacity). Accordingly, the pressure in the crank chamber is adjusted in an autonomous manner. It is to be noted that the target discharge capacity of the compressor is determined based on external information of a temperature setting switch or the like of the air conditioning system.
In general, the electromagnetic solenoid assembly includes a solenoid, movable and fixed cores forming a part of a magnetic circuit, and an operating rod connecting the movable core to the valve member of the valve unit, and the operating rod slidably extends through the fixed core.
The magnetic circuit has to generate only an axial electromagnetic force along an axial direction of the movable core or the operating rod. However, the magnetic circuit generates not only the axial electromagnetic force but also a radial electromagnetic force along a radial direction of the movable core because of a processing or assembling error of each component of the electromagnetic solenoid assembly, and the generation of the radial electromagnetic force cannot be avoided.
Moreover, the larger a cooling load of the air conditioning system, that is, the target discharge capacity of the compressor (the urging force of the valve member) is, the more axial electromagnetic force the electromagnetic solenoid assembly generates. Moreover, with the increase of the axial electromagnetic force, an undesired radial electromagnetic force also increases.
Since the large radial electromagnetic force biases the movable core in a radial direction, a sliding resistance of the operating rod with respect to the fixed core is not uniform in a peripheral direction of the operating rod. Therefore, abrasion of the outer peripheral surface of the operating rod proceeds only partially in the peripheral direction, this non-uniform abrasion obstructs stable sliding of the operating rod, and results in unstable opening/closing operation of the valve member in the valve unit.